Many modern vehicles have "smart alternators" that drop the charge voltage fairly quickly which is fine for the start battery but leads to 2nd batteries being undercharged and failing very quickly.

Dc-dc chargers have been around for a while and are mainly used to over come the voltage drop when charging batteries in caravans etc. These are generally very expensive like anything that is 4x4 related.

I've used 2 of these to boost from 24V to 48V. Look to be a simpler version of one you linked too.One fed a DC POE switch for quite a while without issues. Other was used as a battery charger. Both did the job.